1. Field of the Invention
The present invention relates to a method for manufacturing a triarylpyrazine derivative. In particular, the present invention relates to a method for manufacturing a 2,3,5-triarylpyrazine derivative in which a substituent having an electron-withdrawing property is bound to an aryl group at a 5-position.
2. Description of the Related Art
A display device using a light-emitting element in which an organic compound is used as a light-emitting substance (organic EL element) has been developed rapidly as a next generation display device because it has advantages such as thinness, lightness in weight, high response speed, and low power consumption. Although there have been various obstacles, technique has been improved such that organic EL televisions have become commercially available recently.
In an organic EL element, when voltage is applied between a pair of electrodes which interpose a light-emitting layer, electrons and holes injected from the electrodes are recombined to form an excited state, and when the excited state returns to a ground state, light is emitted. A wavelength of light emitted from a light-emitting substance is peculiar to the light-emitting substance; thus, by using different types of organic compounds as light-emitting substances, light-emitting elements which exhibit various wavelengths, i.e., various colors can be obtained.
In a case of a display device which is expected to display images, such as a display, at least three colors of light, i.e., red, green, and blue are required to be obtained in order to reproduce full-color images. To achieve this, for example, there are following methods: a method in which a light-emitting element emitting light with a light-emitting spectrum in a wide wavelength and a color filter are combined, a method in which a light-emitting element emitting light with a shorter wavelength than a wavelength of an objective color and a color conversion layer are combined, a method in which a light-emitting element emitting light with a desired wavelength is used. Among these three methods, the final one, i.e., a method in which a desired wavelength is obtained directly is preferable because loss in energy is small if the method is used.
This method is adapted to the above-described organic EL televisions which have become commercially available; however, actually, in addition to that method, a color filter is used, and a micro cavity structure is used for a light-emitting element in order to improve color purity. Organic EL televisions have got many advantages but is naturally expected to provide high quality images as a next generation television, and a light-emitting element exhibiting an appropriate emission color is required to live up to the expectation.
A light emitted from a light-emitting substance is peculiar to the substance as described above. There are many measures to improve the color purity of the organic EL television, which means that a light-emitting element which exhibits light emission of a favorable color and also satisfies another components such as a lifetime or power consumption is very difficult to be obtained. In addition, important characteristics of a light-emitting element, such as a lifetime or power consumption, do not necessarily depend on only a substance exhibiting light emission. The characteristics are affected also by layers other than a light-emitting layer, an element structure, an affinity between a light-emitting substance and a host, or the like. Therefore, there is no doubt that many kinds of light-emitting substances exhibiting light emission of a favorable color are needed to show the growth of this field.
In any case, there are not many light-emitting substances exhibiting light emission of a favorable color which is sufficient for productization in the present situation. In view of this present situation, an organometallic complex as shown in Patent Document 1 is proposed as one of substances exhibiting a favorable red light emission (Patent Document 1) from the present applicant.
In this Patent Document 1, it is disclosed that an organometallic complex in which a pyrazine derivative is used as a ligand exhibits a favorable red light. In general, a pyrazine derivative can be obtained by dehydration condensation of α-diketone and diamine, and an oxidative dehydrogenation reaction following the dehydration condensation.    [Patent Document 1] Japanese Published Patent Application No. 2007-284432.